1. Field of the Invention
The present invention relates to an apparatus for peeling a wafer on which semiconductor elements are formed from a reinforcing plate which is bonded to the wafer for increasing the mechanical strength of the wafer. The peeling is performed in the end of the manufacture of a semiconductor wafer having a monolithic microwave integrated circuit used in microwave and milliwave ranges as an MMIC (Microwave Monolithic Integrated Circuit) thereon.
2. Related Background Art
In recent rapid developments of information network systems, strong demand for satellite communication and broadcasting systems have arisen, and the frequency bands are gradually being shifted to higher frequencies. Under these circumstances, extensive studies on MMICs for a variety of practical applications and mainly military and special industrial applications are also shifted to those for commercial applications. While these MMICs include "uniplanar" type MMICs which do not require a thin substrate, generally, various methods for forming wiring lines using microstrip lines are proposed.
In an MMIC formed by the above methods, the thinning of the thickness of a wafer(substrate) causes following advantages.
1 a microstrip line for the same characteristic impedance can have a smaller width, thereby obtaining a compact MMIC; and
2 an etching time for forming via holes can be shortened to minimize variations in shapes of via holes.
For these reasons, the thickness of the wafer is generally reduced to as small as 150 .mu.m to 80 .mu.m.
After the front wafer surface process in which a semiconductor element is formed on and/or into a front surface of the semiconductor substrate is completed, the thickness of a wafer which is a semiconductor substrate is reduced, and etching is performed for the formation of via-holes which pass through the substrate for forming electrical connection between the front surface and a back surface of the substrate. In addition, a back wafer surface process such as metal plating on the back wafer surface is performed. In this process, in order to prevent cracking of the thinned wafer, it is bonded to a reinforcing plate made of quartz glass or silicon with an adhesive such as an electron wax, thereby performing the back wafer surface process while the mechanical strength of the thinned wafer is increased.
In this case, upon completion of the back wafer surface process, the unnecessary reinforcing plate must be removed or peeled from the thinned wafer. Since no appropriate conventional apparatus for removing the reinforcing plate is available, this operation has been manually performed.
When the diameter of a GaAs wafer is increased from 3 to 4 inches, it is very difficult to peel the wafer from the reinforcing plate without any damage to the wafer. A product yield in the wafer peeling process tends to be decreased even by a skilled operator.